Method of operating x-ray device



May 5 1959 GQ DESTRIAU 2,885,559

METHOD OF' OPERATING X-RAY DEVICE Filed March 13, 195'? 2 'sheets-sheet 1 4. c. sven Y y.; BY WQ fm May 5, 1959 G. DEsTRlAU' I 2,885,559

METHQD oF OPERATING X-RAY DEVICE Filed March 15, 1957 2 Sheetsheet 2 INVENTOR. 650/?@55' @ESTR/5 0 United States Patent O METHOD OF OPERATING X-RAY DEVICE Georges Destriau, Cauderan, France, assgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 13, 1957, Serial No. 645,695

11 Claims. (Cl. Z50-71) This invention relates to X-ray-electroluminescent devices and, more particularly, to a method for operating a liuoroscopic system. i In the operation of fluoroscopic systems, the images are produced by irradiating a phosphor screen with an X-ray signal. The brightness of the image which results normally varies according to the intensity of the X-rays striking the iluoroscopic screen. It is desirable to achieve as bright a picture as possible without exposing the object being X-rayed to excessive irradiation, particularly where living organisms are concerned. In addition, it is desirable in some cases to increase the contrast obtainable in .the image since the images are produced by the contrast differences between individual portions thereof. In addition, it is desirable for some limited applications to decrease the contrast in the images produced.

It is the general object of this invention to provide a method for increasing the brightness of a uoroscopic image without substantially increasing the quantity of X- fray irradiation to which the object being X-rayed is ex- `posed.

, It is a further object to provide a method for varying the contrast in the luminous response to an X-ray signal of an X-ray responsive phosphor screen.

It is an additional object to provide a method for enhancing the brightness of a uoroscopic screen without substantially increasing the quantity of X-ray irradiation to which the object being X-rayed is exposed and to vary simultaneously the contrast in the luminous response to Athe X-ray signal of the X-ray-responsive uoroscopic screen.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds,- are achieved by providing a process for operating an X-ray apparatus incorporating an X-ray-responsive phosphor screen characterized by displaying an enhanced luminous output when excited by X-rays and simultaneously placed within the influence of an alternating electric field. In the operation of this apparatus, the phosphor screen is presensitized by applying thereto X-ray irradiation which preferably is of substantially uniform intensity. Simultaneous with the X-ray irradiation an electric field is applied across the screen and the X-ray irradiation and electric field are then removed. Thereafter the screen is irradiated with the X-ray signal which is to be reproduced on the screen and the resulting image will have enhanced brightness, or enhanced brightness with a varied contrast, depending upon the quantity and intensity of the X-ray irradiation to which the screen is exposed.

For a better understanding of the invention reference should be had to the accompanying drawings, wherein:

Fig. l is a sectional elevation of the preferred X-rayelectroluminescent fluoroscopic screen;

Fig. 2 is a schematic diagram of the X-ray unit and operating circuit therefor, illustrating the phosphor screenpresensitizing operation;

Fig. 3 is a schematic diagram similar to Fig. 2 illusltrating the second phase of the equipment operation,

wherein the object image is produced on the tluoroscopic screen;

Fig. 4 is a graph of the ratio of enhanced output vs. X-ray irradiation of a presensitized uoroscopic screen;

Fig. 5 is a graph of brightness in arbitrary units vs. time, illustrating the operation of the unit so that the screen luminesces with a very bright picture and with an enhanced contrast;

Fig. 6 is a graph similar to Fig. 5, but illustrating the operation of the system so that the image produced has an enhanced brightness and the same contrast as would be obtained for a normal liuoroscopic screen;

Fig. 7 is a view similar to Figs. 5 and 6, but showing the operation of the unit so that the image produced has a contrast which is decreased over that which would normally be obtained when irradiating the usual uoroscopic screen.

Although the principles of the invention are broadly applicable to any system wherein an X-ray-responsive phosphor of the type specified herein is to be irradiated by X-rays, the invention has particular reference to lluoroscopic screens which are fabricated similar to an electroluminescent cell and hence it has been so illustrated and will be so described.

In copending application of G. Destriau, the inventor herein, S.N. 433,185, filed May 28, 1954, titled X-Ray Electroluminescent Screen and assigned ,to the present assignee, is disclosed an X-ray-electroluminescent device wherein the output of the X-ray-responsive phosphor is enhanced by the simultaneous application of an electric field across the phosphor. This enhanced output enables a smaller dosage of X-rays to be used in order to achieve a usable brightness of the fluoroscopic screen or, alternatively, makes possible a brighter picture without increasing the dosage of X-rays. The phosphor materials which may be used in this co-pending application are those which will display an enhanced luminous output when excited by X-rays and simultaneously placed within the influence of an alternating electric field. This is contrary to the action of most phosphors which will display a quenching eiect under similar conditions.

The phosphors which may be used in the instant system are those which may be used in the so-called X-ray enhancemen as disclosed in the heretofore-mentioned copending Destriau application, namely, those phosphors which display an enhanced output when irradiated with X-rays and simultaneously placed within the inlluence of an alternating electric iield. Speciiic phosphors which will be suitable for the instant purpose are mixtures of zinc sulde and cadmium sulfide wherein the molar ratio of zinc to cadmium is from nine mole parts zinc, one mole part cadmium to three mole parts zinc, seven mole parts cadmium and activated by from 0.01 102 to 6.O 1()*2 mole of manganese per mole of luminescent material. In addition, the phosphor material may be-activated by a mixture of manganese and silver, with the silver being present in amounts of from traces (O.00l 102 mole silver per mole manganese) up to about 1.0 l02 mole silver per mole manganese. Also, zinc-sulfide phosphors which are activated with manganese or mixtures of manganese and silver in the heretofore-disclosed amounts are also suitable. As a specific example, the phosphor material may comprise 1CdS'3.5ZnS, activated by 1X l0-4I mole manganese per mole of `luminescent material, such a phosphor having been fired during preparation at a temperature of from 800 C. to 1150 C.

In Fig. 1 is illustrated the preferred embodiment of the electroluminescent-lluoroscopic screen 10 which comprises a substantially planar layer of luminescent material 12 adjacent a vsubstantially planar layer of dielect tric material 14 with the luminescent and dielectric material's being sandwiched between two thin, conducting layers or 'electrodes 16 and 18. Each 'of the lelectrode layers 16 and 18 may be connected through suitable bus bars 20 and suitable electrical connection 22 to the `electroluminescent field-voltage supply described hereinafter. A foundation-viewing plate 24 is placed over one of the conducting layers, for example electrode layer 18 and an insulatingdayer 26 may be placed over the `other conducting electrode layer 16 in order to minimize 'shock hazard. A protecting and handling shield 28 may be provided around the entire periphery of the screen in order to facilitate storage, handling, etc.

The luminescent material layer 12 is preferably positioned next to the foundation-viewing plate 24, although Ifor 'some applications it may be preferable to place the dielectric layer 14 next to the viewing Aplate 24. The thickness of the luminescent material layer 12 is not particularly critical, but as a specific example, it may have a thickness of 0.2 mm. The dielectric layer 14 may comprise any suitable dielectric which has a high dielectric constant, is transmissive to either visible light or to X-rays depending upon its position within the screen, and will not deteriorate rapidly under the action 'of `X-rays. Such materials are well known and as an example, the dielectric material layer 14 may comprise 'a mica sheet about 0.05 mm. thick, although this thickness is in no way critical and may be increased or decreased as indicated by the application.

Alternative constructions are also possible in the screen 10 and -a suitable light-transmissive dielectric material such as polyvinyl-chloride acetate may be admixed with the phosphor and the separate layer of dielectric dispensed with, if desired, or the dielectric material may be dispensed with entirely in some special applications and only the phosphor layer 12 placed between the electrodes 16 and 18. It should be pointed out that the purpose of the dielectric material is to prevent electrical breakdown through the phosphor and between 'the electrodes 16 and 18 and the electric elds as may be used herein need not be particularly intense. The usable electric iields, however, may vary over a wide range as in the heretofore-mentioned copending De'striau application and as a specific example, the electric eld which is applied across the screen during screen presensitization may have an intensity of 20 kv. per cm.

The conducting electrodes 16 and 18 may be fabricated of any conducting materials which may be coated as a thin sheet and are transmissive to visible light in the case of the lower layer 18 and transmissive to X- rays in the case of the upper layer 16. Of course, these electrodes should not deteriorate appreciably under the action of X-rays. As an example, the electrode 18 may be fabricated of a thin layer of tin oxide on a glass base, such as sold under the trademark Nesa by Pittsburgh `P1ate Glass Co., Pittsburgh, Pa. Other suitable thin conducting coatings such as oxides of zinc, cadmium, aluminum or bismuth, for example, may also be used. The electrode 16 may be fabricated of tin oxide, for example, or it may be a thin coating of aluminum which may be applied by the well-'known vacuum-metalizing techniques. The thin protective layer 26, which is intended to insure against shock hazard and to facilitate handling, may be fabricated of any X-ray transmissive material which has relatively good electrical insulation properties and plastics such as polytetrauoroethylene are suitable. The protective layer 26 may be dispensed with, if desired, and the shock hazard eliminated by grounding the electrode 16.

The foundation glass-viewing plate is normally fabricated of any glass which contains heavy atoms which will absorb the X-rays and thus protect the viewer or .the photographic plate, as the case may be. As an example, any of the well-known lead or cerium glass may he used. The protecting and handling shield 28 maybe fabricated of a plastic similar to the layer 26 and this shield may be dispensed with, if desired.

In Fig. 2 is illustrated, in block diagram, one embodiment of a suitable X-ray apparatus which in this showing is set for initial exposure of the object being X-rayed in order to presensitize the uoroscopic screen 10. This apparatus 30 comprises an X-ray rectifier and transformer unit 32, X-ray and iilm shutter timer 34, X-ray tube 36, iield-voltage-control unit 38, field-timer unit 40, the X-ray fluoroscopic screen 10, exposure switch 42, electric-field switch 44, camera lm 46, camera-shutter tripping unit 48 and camera shutter 50. All of the components of this apparatus are well known with the exception of the X-ray-uoroscopic screen 10 which has been described in detail hereinbefore, and which screen may be identical, if desired, with the corresponding screen described in the heretofore-mentioned copending Destriau application. Also, the use of automatic timers may be eliminated, if desired, and the entire timing sequence may be carried out by hand.

In Fig. 3 is shown in block diagram `the same X-jray apparatus as is shown in Fig. 2, but with the electric tield switch 44 in open position. With the X-ray iiuoroscopic screen presensitized, the apparatus is thus set to irradiate `the object being X-rayed with X-rays which preferably are relatively intense, in order to produce on the fluoroscopic screen a very bright and transient luminous image, as will be explained more fully herein after. The details of the operation of this apparatus will be considered as the description proceeds. For purposes of explanation, the object 52 being X-rayed will be assumed to be comprised of two portions of different X-ray permeability.

In explanation of the term screen presensitization it has been found that when a fluoroscopic screen of the type described herein is iradiated with X-rays of substantially uniform intensity and simultaneously placed within the influence of an alternating field, a portion of the luminous response developed by the screen-applied X-rays will be imparted to the screen and in effect stored This is termed screen presensitization. yThis screen-imparted X-ray irradiation may be released from the so-called presensitized screen by a second X-ray irradiation and the intensity of the stored X-ray irradiation which will be released is dependent upon the intensity of the second X-ray irradiation. If a signal 4is thus generated by irradiating an object which has varying permeability to X-rays, the intensity of the X-ray irradiation striking the screen will vary according to the X-ray permeability of the object and the screenstored energy may thus be used to reproduce the image which corresponds to the X-ray signal. Presensitization is not effected by the field alone, nor will the field alone, as specified, develop an appreciable .pure electrolnrninescence.

In copending application of G. Destriau, the inventor herein, titled X-Ray System, S.N. 645,694, led concurrently herewith and assigned to the present assignee, is described an X-ray apparatus similar to the instant apparatus and a method for operating same wherein the screen is presensitized by applying thereto an X-ray signal and an electric lield. Thereafter the stored signal may be released by substantially uniform intensity X- rays. The instant method dilers from the method disclosed in this concurrently filed and copending appli cation, since in the instant method the screen is presensitized by irradiating the screen with X-rays which preferably are of substantially uniform intensity while the screen is within the inuence of an alternating electric iield. In copending application of G. Destriau, the inventor herein, tilted X-Ray Method, S.N. 645,742, led concurrently herewith and assigned to the present assignee is described an X-ray apparatus which is also similar tothe instant apparatus and a .method for operat- 15 ing same wherein the screen is presensitized by applying thereto an alternating electric field and the X-ray signal.v Thereafter, the X-ray signal is again applied'to the screen. The instant method is also to be distinguished from the method disclosed in this latter concurrentlyfiled and copending application since the screen-presensitization step difers.

In Fig. 4 is shown a graph of enhancing ratio vs. second X-ray irradiation, expressed vas milliamperes of current drawn by the X-ray tube 36. In arriving at these curves, the screen 10 was presensitized` and the screen brightness was measured with no object between the screen and the X-ray tube when it drew the indicated currents. Of course, inclusion of an X-ray absorptive object between the screen 10 and tube 36, after the screen has been presensitized, requires a greater intensity of X-ray irradiation to deliver to the screen 10 an equivalent intensity of X-rays. y

Each of the curves in Fig. 4 indicates the relative brightness ratio for a different presensitizing quantity (Q) of X-rays, as follows: Curve A, Q=640 micro-. ampere minutes (,ua. min.); curve B, Q=320 tta. min.; curve C, Q=l60 na. min.; curve D, Q=80 na. min.; curve E, Q=4O ya. min.; curve F, Q=20 na. min.; curve G, Q=10 na. min.; curve H, Q=5 ,ua. min. The brightness ratio is also dependent upon the intensity of thev second X-ray irradiation of the screen, which in the instant method takes the form of an X-ray signal, and this is plotted as the abscissa in these curves. In the relative brightness ratio, Bm is the maximum brightness in arbitrary units for a presensitized screen and B is the maxi mum brightness in arbitrary units for an unsensitized screen irradiated with equal-intensity X-rays,

The X-ray tube 36 as used herein had a hard glass window and was operated at a voltage of 80 kv. with a self-rectified circuit. The distance from the centerline of the tube to the screen 10 was 20 cm. Under these conditions of operation, the tube current and time were measured to the indicated values of Q (quantity of X-rays) and j (tube current). It should be understood that the foregoing example of operating conditions may be modified as indicated by the application. Also the quantity Q of presensitizing X-rays may be obtained by means of a more intense X-ray irradiation for a shorter time, for example.

In Fig. 5 is illustrated the operation of the equipment in order to achieve a very bright signal without appreciably increasing the quantity of X-rays applied to the object being X-rayed and in addition, Fig. 5 illustrates the operation of the equipment in order to obtain a very high degree of contrast in the image produced on the screen. For purposes of a simplified explanation, the object 52 being X-rayed may comprise two portions, one portion of which has seven times the permeability `to X-rays as the other portion. The screen is first presensitized by applying thereto an X-ray irradiation, which preferably has substantially uniform intensity, for a sufiicient period so that the quantity of X-rays striking the screen is 160 na. min. An electric field is simultaneously applied across the screen with the X-ray irradiation and the field is preferably removed shortly after the X-ray irradiation in orderto avoid desensitizing the presensitized screen. The brightness of the screen during the presensitization will follow the curve O-M-N and the field is preferably removed at point P which may be 10 seconds, for example, after the X ray irradiation is stopped. Thereafter the object which is to be X-rayed is placed between the X-ray tube ,-36 and the screen 10 and relatively intense X-rays are applied to the object to generate an X-rayv signal which is applied to the screen. Assuming that the X-ray irradiation intensity which passes the more X-ray-transmissive portions of the object is equivalent to an X-ray intensity of j=1.4 milliamperes tube current, the brightness of the screen will follow the curve O-R-S. Without the screen presensitization, the brightness of the screen would follow the dotted line04. At point S, the transient image, which represents the stored luminous energy, will be substantially expended. It has been assumed that the body is comprised of two portions, one portion of which is seven times as permeable or as transmissive to X-rays as the other portion and under such X-ray irradiation, the screen portions which are adjacent the more X-ray opaque portion of the body will receive an X-ray irradiation equivalent to j=0.2 milliampere. This will cause thescreen to luminesce in these portions with a brightness which will follow the general curve O-R-S and at point S' the stored luminous energy will be substantially expended. It should be pointed out that if the screen were not presensitized, the brightness under an equivalent X-ray irradiation would follow the dotted curve O-S'. Referring to Fig. 4 and in particular curve C in Fig. 4, when a screen presensitized to a Q of pa. min. is irradiated with an X-ray intensity equivalent to 1.4 milliamperes drawn by the X-ray tube, the brightness ratio Bm divided by B0 will be approximately 2.66: 1. When the screen which is presensitized to a Q of 160 ya. min. is irradiated with an X-ray intensity equivalent to a current j of 0.2 milliampere drawn by the tube, the brightness ratio of Bm/Bo will be approximately 1.5:1. This difference in brightness ratios will cause the contrast between--the brightest and darkest portions of the image to be 12.4:1 rather than 7:1 as it would be if the screen were not presensitized.

It should be pointed out that the brightness of the image produced on the screen during the second X-ray irradiation, when thescreen is irradiated by the X-ray signal to causefit to lrelease the stored energy, is not as great as would be' obtained with the simultaneous application of an electric field across the screen when the 'i screen is irradiated with equivalent intensity X-rays. In

explanation, the best brightness ratio which has been achieved in a released image is about 2.66:l while a brightness enhancement of from 4 to 5:1 and greater has been achieved where the field is simultaneously applied across the phosphor with the X-ray signal. The build-up in luminosity-of the enhanced brightness where the field is simultaneously applied, however, is relatively slow and accordingly, the quantity of X-rays required to produce such ultimate enhanced luminosity is correspondingly great. In the instant system, the buildup in luminosity of the screen, upon application of the intense X-ray signal, is quite rapid since the presensitizing energy is being released. To minimize the quantity of X-rays which are applied to the object, immediately after the peak in luminosity for the released energy has been reached, the X-ray signal irradiation of the screen may be stopped and the total quantity of the X-rays to which the object is exposed need only be relatively small in order to obtain a relatively bright image.

It should be pointed out that the more intense the X-ray signal irradiation, the more transient the released energy becomes and it is preferable to record photographically this released energy in order that it may be studied later. Referring to Fig. 3, when the switch 44 is raised to an elevated position to open the field timer unit 40, it renders operative the camera-shutter-tripping unit 48. When the exposure switch 42 is closed, the unit 34 is actuated and at a predetermined time thereafter, the shutter-tripping unit 48 actuates the film shutter 50 to record the brightest portions of the transient image. Immediately thereafter the X-ray signal irradiation may be stopped and this may be effected by opening the exposure switch 42 -orby setting the timer unit 34. As an example, the camera may record the image five seconds after the X-ray signal irradiation of the screen 10 is started.

In Fig. 6 is illustrated the operation of the unit wherein the contrast in the image produced on the screen is maintained the same as what it would be with the usual operation of a fiuoroscopic screen. In this operation of the unit, the screen 10 is presensitized as previously explained,

D, Fig. 4).

7 but toa t'otaVQ 4of 8G pa. min.,ifor example "('see'c'urve Thereafter, 'an object isl placed between the tube 36 and the screen 10 and `for purposesof illustration, the ratio of permeability to X-rays of two portions comprising the object have been assumed to be 13:7. Again referring to Fig. 4, curve D, with an X-ray intensity applied to the object so that the equivalent intensity of j=1.3 milliamperes strikes the screen adjacent the more X-ray transmissive portions of the object, the rratio of Bm divided by B will be about 1.9. With this same object and X-ray irradiation, the intensity of the X-ray striking the screen adjacent the more X-ray opaque portions of the object will have an intensity equivalent to f1-0,7 milliamp. and as shown in curve D, the ratio of Bn divided by B0 is still about 1.9. Under these conditions of operation, the contrast between the brighter and darker portions of the screen will remain the same as that 'contrast which would be achieved with no screen presensitization. In the operation of the unit as illustrated in Fig. 6, the brightest portions of the transient image (points T and T) may be recorded photographic'ally as explained hereinbefore. Of course, without screen presensitization the screen brightness under the indicated X-ray signal irradiation would follow Vthe dotted curves in Fig. 6.

In Fig. 7 is illustrated the operation of the -system whereby the contrast between individual portions of the image may be decreased. In order to simplify the explanation, the object 52 being X-rayed has been assumed to be comprised of two portions, one of which has seven times the permeability to X-rays as the other portion. The screen is iirst presensitized to a total Q of 2O ya. min., see curve F in -Fig. 4. Thereafter Ythe object is placed between the X-ray tube and the screen 'and irradiated with X-rays of such intensity that the screen `portions adjacent the more X-ray transparent portion of the object will receive an X-ray intensity equivalent 'to j=1.4 milliamps. Under these conditions of operation, the ratio of Bm divided by Bo will be 1.06- With the same intensity of X-ray irradiation, the portions of the screen 10 adjacent the more X-ray opaque vportion of the object will receive an X-ray irradiation equivalent to "j=0.2 milliamp. and will cause the presensitized screen 10 to display a brightness ratio of Bm dividedby B0 of 1.5 The brightest and darkest portions of the image (points -U and U', Fig. 7) thus display a contrast ratio of 4.9:1 as compared to the ratio of 7:1 which would normally be expected if the screen were not presensitized. As before, without screen presensitization the screen brightness under the indicated X-ray signal `irradiation would follow the dotted curves in Fig. 7. Of course, the transient portions of the released luminous energy may be recorded photographically as hereinbefore described.

tion of the stored energy. It should be pointed out, howf ever, that irradiation of the presensitized screen with visible light or ultraviolet will impair the presensitization.

lt will be recognized that the objects of the invention have been achieved by vproviding a method for achieving a very bright iluoroscopi'c image while exposing the object being X-rayed to a minimum quantity of X-ray irradiation. In addition, the screen presensitization may be so selected as to either 'increase or decrease the contrast obtainable in the image, if desired.

In the foregoing examples, the screen 10 has been presensitized with substantially uniform intensity X-'rays and such a procedure will normally be desirable. For

some purposes, however, it may be desirable to presensitizc the screen with non-uniilorm-intensity X-rays -so that diierent yportions :of the screen will display different ness ratios under later irradiation by an X-ray signal. This may readily be achieved by presensitizing the screen with an appropriate X-ray filter between the X-ray tube and a portion of the screen 10 so that the upper portions of the screen may be presensitized to a Q of 160 na: min., for example, and the lower portions of the screen may be presensitized to a Q of tra. min., for example. Under later X-ray signal irradiation, diierent portions of the screen will respond with a different brightness ratio as readily determined from Fig. 4, curves C 'and D.

In the foregoing examples, the screen presensitizing eld has been removed shortly after the presensitizing X-rays have been stopped. It should be understood that the iield and presensitizing X-rays could be removed substantially simultaneously, if desired, without impairing the operation. If the presensitizing X-rays are removed after the viel'd is removed, the energy stored in the presensitized screen will be reduced correspondingly.

While in accordance with the patent statutes, one best- -known embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

Iclaim:

l. The process of enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output 'when irradiated by X-rays and simultaneously placed within the influence of an alternating electric iield, said process comprising applying to said screen a quantity of X-ray irradiation and-simultaneously Yapplying across said screen an alternating electric eld, removing from -said screen said applied X-ray irradiation and said applied electriciield, passing relatively intense X-rays through an object having varying permeability to X-rays to generate an X-ray signal, and applying said vvX-ray signal to said screen to generate thereon an intense and transient luminous image.

2. The process of enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output vwhen -irradiated by X-rays and simultaneously placed within the influence of an alternating electric eld, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said Vscreen an alternating electric eld, removing from said screen said applied X-ray irradiation and said applied electric fleld, passing relatively intense X-rays through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image.

3. The process of enhancing the luminous response to an X-ray `signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the inlluence of an alternating electric iield, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field, removing from said screen said applied X-ray irradiation and said-applied electric ield, passing relatively intense X-rays through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal-to 'said screen to generate thereon an intense and transient luminous image, and recording said intense and transient luminous image.

4. The process of enhancing the luminous response to an-X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising aplying to said screen a preselected quantity'of'X-ray irradiation and simultaneously applying across said screen an alternating electric iield, removing from said screen said applied X-ray irradiation, thereafter removing from said screen said applied electric field, passing relatively intense X-rays through an object having varying permeability to X-rays to generate an X-ray sig nal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image.

5. The process of enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiaetd by X-rays and simultaneously placed within the influence of an alternating electric iield, said process comprising applying to said screen a quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field, removing from said screen said applied X-ray irradiation and substantially simultaneously removing said applied electric field, passing relatively intense X-rays through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image.

6. The process of varying the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric eld, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation and said applied electric field, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X-ray signal, whereby an enhanced luminous image with Varied contrast is produced on said screen.

7. The process of increasing the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric eld to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation and said applied electric field, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X-ray signal, whereby an enhanced luminous image with increased contrast is produced on said screen.

8. The process of decreasing the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric eld, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation and said applied electric eld, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X-ray signal, whereby an enhanced luminous image with decreased contrast is produced on said screen.

9. The process of varying the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric eld to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation and said applied electric eld, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X-ray signal, and recording said transient luminous image.

l0. The process of varying the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the influence of an alternating electric field, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation, thereafter removing from said screen said applied electric field, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X- ray signal, whereby an enhanced luminous image with varied contrast is produced on said screen.

ll. The process of varying the luminous contrast and enhancing the luminous response to an X-ray signal of an X-ray responsive phosphor screen characterized by displaying an enhanced luminous output when irradiated by X-rays and simultaneously placed within the inuence of an alternating electric field, said process comprising applying to said screen a preselected quantity of X-ray irradiation and simultaneously applying across said screen an alternating electric field to presensitize said screen to a preselected degree, removing from said screen said applied X-ray irradiation and substantially simultaneously removing said applied electric field, passing X-rays of preselected relatively high intensity through an object having varying permeability to X-rays to generate an X-ray signal, and applying said X-ray signal to said screen to generate thereon an intense and transient luminous image having luminous contrast corresponding to the degree of said screen presensitization and the intensity of said X-ray signal, whereby an enhanced luminous image with varied contrast is produced on said screen.

References Cited in the file of this patent Electroluminescence and Related Topics, by Destriau and Ivey, Proceedings of the IRE, December 1955, pp. 1,911 to 1,937. 

